如何访问我无法修改的类中的包保护变量

Question

I have a variable that is in a package, where I can neither modify the package or that class and I need to access it is there any way I can do this. I can not modify com.archi.hello or the contents of it

For Example:

com.archi.hello:

class obj:

public class obj () { 
    int j = 123;
    int getJ () {
        return j;
    } 
}

com.archi.newpackage:

public class getJo () { 
    int jo;
    obj obj = new obj();
    jo = obj.getJ(); // THIS DOES NOT WORK BECAUSE THE GETTER IS NOT 
    PUBLIC 
}

I need to set jo to j without modifying com.archi.hello in any way, and yes i have tried extending the obj. Is there anyway to do this?

Answer 1

There are 2 possible cases to get value of j :
Case 1: Because in your example, class obj is public and int j with default visibility => j as a public. Read this about default access modifier

public class obj () { 
    int j = 123; // not declared modifier => modifier is public because obj class is pulic
    int getJ () { // this method is private
        return j;
    } 
}

just do thiss to get value of j :

obj objInstance = new obj();
int valueOfJ = objInstance.j;

Case 2: private int j with private access modifier so it is invisible completely with outside. In the encapsulation priciple of Java, it not allow to access or modify j official way. But, you can use some trick to get value j .

public class obj () { 
    private int j = 123; // declared modifier => modifier is private
    int getJ () { // this method is private
        return j;
    } 
}

How to get j

obj objInstance = new obj();
java.lang.reflect.Method method = objInstance.getClass().getDeclaredMethod("getJ");
method.setAccessible(true);
int valueOfJ = (int)method.invoke(objInstance);